1. Field of the Invention
This invention relates to improvements in or relating to a brush holding device for use with an electric rotary machine.
2. Description of the Prior Art
An exemplary one of conventional brush holding devices for use with an electric rotary machine is disclosed, for example, in Japanese Utility Laid-Open No. 62-145454. The conventional brush holding device is first described with reference to FIGS. 4 and 5. The brush holding device includes a pair of negative (-) side brush holding frames 2a and 2b and another pair of positive (+) side brush holding frames 3a and 3b all formed from steel plates and disposed for sliding contact with a commutator 1. The positive side brush holding frames 3a and 3b are securely mounted at pairs of riveted fixing portions 5a and 5b thereof on a pair of mounting plates 4a and 4b, respectively. The mounting plates 4a and 4b are made of an electrically insulating synthetic resin material.
The negative-side brush holding frames 2a and 2b are securely mounted directly on a base plate 6 formed from a steel plate while the positive side brush holding frames 3a and 3b are securely mounted at pairs of riveted fixing portions 14a and 14b on the base plate 6 by way of the mounting plates 4a and 4b, respectively.
A pair of positive side brushes 7a and 7b are accommodated in spacings defined by the positive side brush holding frames 3a and 3b and the mounting plates 4a and 4b, respectively. Another pair of negative side brushes 8a and 8b are similarly accommodated in spacings defined by the negative side brush holding frames 2a and 2b and the base plate 6, respectively. The negative side brushes 8a and 8b are connected to the base plate 6 by way of a pair of negative side lead wires 9a and 9b, respectively. The negative side brushes 8a and 8b are electrically grounded by way of the base plate 6 formed from a steel plate and an end bracket (not shown) of a rotary machine in which the brush holding device is incorporated.
Meanwhile, the positive side brushes 7a and 7b and a connector 12 are connected to a power source not shown by way of a pair of positive side lead wires 10a and 10b.
The brushes 7a, 7b, 8a and 8b are normally urged into sliding contact with an outer periphery of the commutator 1 by respective brush springs 11. The base plate 6 is mounted on the aforementioned end bracket of the rotary machine by means of a female screw 13.
The conventional brush holding device is constructed in such a manner as described above. Thus, since the positive side brushes 7a and 7b are accommodated between the positive side holding frames 3a and 3b and the mounting plates 4a and 4b, respectively, and the mounting plates 4a and 4b are in turn securely mounted on the base plate 6 by riveting in such a manner as to establish an electrically isolated condition of the brushes 7a and 7b, the brush holding device includes a comparatively great number of components. Further, since the holding frames 3a and 3b are securely mounted on the mounting plates 4a and 4b, respectively, by riveting and the plates 4a and 4b are in turn securely mounted on the base plate 6 by riveting, the brush holding device is produced by way of a comparative large number of working steps. Besides, since the holding frames 2a, 2b, 3a and 3b are steel plate articles formed by bending of steel plates, there is a problem that they are likely to become rusty to cause the holding frame 2a, 2b, 3a or 3b to stick to the brush 7a, 7b, 8a or 8b.